Frequency domain unscheduled transmission in a TDD wireless communications system

Abstract

An apparatus and method exploits a variable frequency response of a radio channel in a time division duplex wireless communication system such that for unscheduled uplink transmissions, the transmission power required for correct reception of the data is minimized. The degree of interference caused to other users in both the serving cell and the neighbor cells is correspondingly reduced and hence system capacity is improved.

1. A method of selecting, by a mobile terminal, including a wireless receiver, a signal processor, control logic, and a wireless transmitter, in a TDD wireless communication system, a sub-range of frequencies for uplink transmission from a plurality of sub-ranges of frequencies for uplink transmission, comprising:
 receiving, via the wireless receiver, a downlink signal that has been transmitted over a range of frequencies, comprising a plurality of sub-ranges of frequencies representative of the plurality of sub-ranges of frequencies for uplink transmission, the downlink signal having a known structural aspect as transmitted; 
 determining, by the signal processor, a frequency response of the radio channel through which the downlink signal has passed by comparing the structural aspect of the received downlink signal with the known structural aspect of the downlink signal as transmitted; 
 estimating, by the control logic, at least one path loss metric for at least one of the sub-ranges of frequencies for uplink transmissions based on the frequency response of the radio channel; and 
 selecting, by the control logic, at least one of the sub-ranges of frequencies for uplink transmission, based on the at least one path loss metric. 
 
     
     
       2. The method of  claim 1 , further comprising transmitting, via the wireless transmitter, an unscheduled uplink transmission in the at least one of the selected sub-ranges of frequencies for uplink transmission. 
     
     
       3. The method of  claim 2 , wherein the unscheduled uplink transmission is transmitted, via the wireless transmitter, within a channel coherence time of receiving the received downlink signal. 
     
     
       4. The method of  claim 1 , wherein the downlink signal,received via the wireless receiver, is a reference signal comprising a known sequence of modulation symbols, and wherein the frequency domain response, determined by the signal processor, of the radio channel through which the reference signal has passed is determined using a Fourier Transform of an impulse response of the radio channel as determined from the received downlink signal and the known transmitted downlink signal by a technique chosen from a group of techniques consisting of (i) deconvolution, (ii) matched filter channel estimation, and (iii) correlation. 
     
     
       5. The method of  claim 1 , wherein the frequency domain response, determined by the signal processor, of the radio channel through which the downlink signal has passed is determined by comparing a power spectral density of the downlink signal as received with a known power spectral density of the downlink signal as transmitted. 
     
     
       6. The method of  claim 1 , wherein the frequency domain response, determined by the signal processor, of the radio channel through which the downlink signal has passed is determined by a blind channel estimation technique. 
     
     
       7. The method of  claim 1 , further comprising adjusting, by the control logic, the unscheduled uplink transmission power based on the at least one path loss metric. 
     
     
       8. The method of  claim 7 , further comprising estimating by the control logic, an absolute radio channel path loss value for at least one sub-range of the frequencies, comprising:
 measuring, by the control logic, a received downlink signal power level representative of the at least one sub-range of frequencies, having a known transmission power level, to estimate a radio channel path loss; and 
 setting, by the control logic, a transmission power level for the unscheduled uplink transmission based upon the estimated radio channel path loss over the sub-range of frequencies. 
 
     
     
       9. A computer-readable medium encoded with computer-executable instructions for performing a method of selecting, by a mobile terminal in a TDD wireless communication system, a sub-range of frequencies for uplink transmission from a plurality of sub-ranges of frequencies for uplink transmission, wherein the instructions are executable by a processor, the computer-executable instructions comprising instructions for:
 receiving a downlink signal that has been transmitted over a range of frequencies, comprising a plurality of sub-ranges of frequencies representative of the plurality of sub-ranges of frequencies for uplink transmission, the downlink signal having a known structural aspect as transmitted; 
 determining a frequency response of the radio channel through which the downlink signal has passed by comparing the structural aspect of the received downlink signal with the known structural aspect of the downlink signal as transmitted; 
 estimating at least one path loss metric for at least one of the sub-ranges of frequencies for uplink transmissions based on the frequency response of the radio channel; and 
 selecting at least one of the sub-ranges of frequencies for uplink transmission, based on the at least one path loss metric. 
 
     
     
       10. The computer-readable medium of  claim 9 , further comprising computer-executable instructions for transmitting an unscheduled uplink transmission in the at least one of the selected sub-ranges of frequencies for uplink transmission. 
     
     
       11. The computer-readable medium of  claim 9 , further comprising computer-executable instructions for the transmission of the unscheduled uplink transmission within a channel coherence time of receiving the received downlink signal. 
     
     
       12. The computer-readable medium of  claim 9 , wherein the downlink signal is a reference signal comprising a known sequence of modulation symbols, further comprising computer-executable instructions to determine the frequency domain response of the radio channel through which the reference signal has passed using a Fourier Transform of an impulse response of the radio channel as determined from the received reference signal and the known transmitted reference signal by a technique chosen from a group of techniques consisting of (i) deconvolution, (ii) matched filter channel estimation, and (iii) correlation. 
     
     
       13. The computer-readable medium of  claim 9 , further comprising computer-executable instructions to determine the frequency domain response of the radio channel through which the downlink signal has passed by comparing a power spectral density of the downlink signal as received with a known power spectral density of the downlink signal as transmitted. 
     
     
       14. The computer-readable medium of  claim 9 , further comprising computer- executable instructions to determine the frequency domain response of the radio channel through which the downlink signal has passed is determined by a blind channel estimation technique. 
     
     
       15. The computer-readable medium of  claim 9 , further comprising computer- executable instructions to adjust the unscheduled uplink transmission power based on the at least one path loss metric. 
     
     
       16. The computer-readable medium of  claim 15 , further comprising computer-executable instructions for estimating an absolute radio channel path loss value for at least one sub-range of the frequencies, comprising: measuring a received downlink signal power level representative of the at least one sub-range of frequencies, having a known transmission power level, to estimate a radio channel path loss; and setting a transmission power level for the unscheduled uplink transmission based upon the estimated radio channel path loss over the sub-range of frequencies. 
     
     
       17. A mobile terminal for a TDD wireless communication system, capable of selecting a sub-range of frequencies for uplink transmission from a plurality of sub-ranges of frequencies for uplink transmission, comprising:
 a wireless receiver capable of receiving a downlink signal that has been transmitted over a range of frequencies, comprising a plurality of sub-ranges of frequencies representative of a plurality of sub-ranges of frequencies for uplink transmission uplink transmission resources, the downlink signal having a known structural aspect as transmitted; 
 a signal processor to determine a frequency domain response of the radio channel through which the downlink signal has passed by comparing the structural aspect of the received downlink signal with the known structural aspect of the reference signal as transmitted; and 
 control logic to estimate a path loss metric for at least one of the sub-ranges of frequencies based on the frequency domain response of the radio channel to select at least one of the sub-ranges of frequencies for uplink transmission, based on the at least one path loss metric. 
 
     
     
       18. The mobile terminal of  claim 17 , further comprising a wireless transmitter operative to transmit an unscheduled uplink transmission in the at least one of the sub-ranges of frequencies for uplink transmission. 
     
     
       19. The mobile terminal of  claim 18 , in which the wireless transmitter is further operative to transmit an unscheduled uplink signal within a channel coherence time of the received downlink signal. 
     
     
       20. The mobile terminal of  claim 17 , further comprising a signal processor operative to calculate by deconvolution an impulse response of the radio channel using the received downlink signal and the downlink signal as known to be transmitted, and subsequently perform a Fourier Transform to calculate the frequency response of the radio channel. 
     
     
       21. The mobile terminal of  claim 17 , further comprising a signal processor operative to determine a frequency domain response of the radio channel through which the downlink signal has passed is determined by comparing a power spectral density of the downlink signal as received with a known power spectral density of the downlink signal as transmitted. 
     
     
       22. The mobile terminal of  claim 18 , further comprising control logic operative to adjust the unscheduled uplink transmission power based on the at least one path loss metric. 
     
     
       23. The mobile terminal of  claim 22 , further comprising control logic operative to estimate an absolute radio channel path loss value for at least one sub-range of the frequencies by measuring a received reference signal power level within the at least one sub-range of frequencies, having a known transmission power level, to estimate a radio channel path loss; and setting a transmission power level for the unscheduled uplink transmission based upon the estimated radio channel path loss over the sub-range of frequencies.